1. Field of the Invention
The present invention relates to an image processing method for conversion of image data, and to an apparatus therefor.
2. Related Background Art
Among such image processing methods, there are already known electronic platemaking in the printing industry, and a professional laboratory technology utilizing computerized photographic image processing in photographic laboratories.
In such image processing, for example in the case of obtaining a reproduced image by photoelectrically scanning an original image with a high-precision scanner such as a layout scanner or a laser color printer, an image processing unit is inserted in the image reproduction process to effect various processes on the input density signal, such as gamma correction, modification of tonal rendition, color correction, image cutout and image synthesis, thereby achieving the following functions:
(1) restoration of faded colors of a color film;
(2) correction of rendition in highlight and shadow areas and emphasis in colors;
(3) salvage of defective image resulting from a failure in the equipment, error in photographing or in film processing; and
(4) formation of a creative image for expanding the area of images or for creation of a new design.
Such special processing is executed on a digital image signal such as a density signal or luminance signal obtained by photoelectrically scanning an original film image with a high-precision color scanner, a color imaging tube or a solid-state color image sensor such as a CCD.
Among such special effects there are already known a mosaic processing for obtaining regularly arranged image, blocks, and posterization and solarization for varying the gamma curve in an unrealistic manner. However, these effects are not enough for expressing a creative image such as is desired for expanding the area of images and creating novel designs. There are also known other functions such as image cutout, image synthesis and painting as achievable with such as equipment DPB7000 (Quontel), Artron 2000 (Artronics) or Response 300 (Scitex). However, these functions, which are achieved by the operator by adding images to the original image by means of a coordinate designating device such as a tablet digitizer, require considerable time, and the skill or sense of the operator is inevitably reflected in the resulting image.
In the following there will be explained the mosaic process.
Let us consider a case of forming a mosaic block of 5 pixels in the x-direction and 5 pixels in the y-direction. Pixel information at a pixel position (m, n) is represented by a(m, n), which is a digital value obtained by an A/D conversion of the density signal or luminance signal of the original film image. In a mosaic process, there is obtained the following relationship between the pixel information a(m, n) of the original image and the pixel information a'(m, n) after processing: EQU a'(5m-i, 5n-j)=a(5m-3, 5n-3)
wherein i=0, 1, 2, 3, 4; j=0, 1, 2, 3, 4; and m and n are positive integers.
In the above-mentioned relationship the central value in a block of 5.times.5 pixels is taken as the representative value and is used in other pixels of the block, but said representative value may be obtained from any pixel in the block or may be the average value of the block.
However, such conventional mosaic process for obtaining regularly arranged blocks is associated with the following drawbacks, and an improvement has been desired in order to obtain a creative image:
(1) the arrangement of rectangular blocks is excessively regular; and
(2) as the pixels in a block have the same value, the obtained image lacks necessary information in the areas where the original image requires a fine expression (areas with much information having high-frequency components).
In order to resolve these drawbacks, the assignee of the present invention has proposed, in U.S. patent application Ser. No. 007,785, a method of varying the shape of a mosaic pattern according to certain parameters such as the spatial frequency or contrast of the image.